Oxidation structure/method to fabricate a high-performance magnetic tunneling junction MRAM

ABSTRACT

An MTJ (magnetic tunneling junction) MRAM (magnetic random access memory) has a tunneling barrier layer of substantially uniform and homogeneous Al 2 O 3  stoichiometry. The barrier layer is formed by depositing Al on a CoFe layer or a CoFe—NiFe bilayer having an oxygen surfactant layer formed thereon, then oxidizing the Al by radical oxidation. The underlying surfactant layer contributes oxygen to the bottom surface of the Al, forming an initial amorphous Al 2 O 3  layer. This layer produces small, uniform grains in the remaining Al layer, which promotes a uniform oxidation of the Al between its upper and lower surfaces by the subsequent radical oxidation. A final annealing process to set a pinned layer magnetization enhances the homogeneous oxidation of the layer.

RELATED PATENT APPLICATION

This application is related to Ser. No. 10/371,841, filing date is Feb.10, 2003, patent number is U.S. Pat. No. 6,703,654, Ser. No. 10/768,917,filing date is Jan. 30, 2004, Ser. No. 10/661,038, filing date is Sep.12, 2003, Ser. No. 10/844,171, filing date is May 12, 2004 and Ser. No.10/849,310, filing date is May 19, 2004, assigned to the same assigneeas the current invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to magnetic tunneling junction (MTJ)MRAMs and more particularly to the use of an oxidation process thatleads to a smooth bottom electrode and resulting superior performanceproperties.

2. Description of the Related Art

The magnetic tunneling junction device (MTJ device) is essentially avariable resistor in which the relative orientation of magnetic fieldsin an upper and lower magnetized electrode controls the flow ofspin-polarized tunneling electrons through a very thin dielectric layer(the tunneling barrier layer) formed between those electrodes. Aselectrons pass through the lower electrode they are spin polarized byits magnetization direction. The probability of an electron tunnelingthrough the intervening tunneling barrier layer then depends on themagnetization direction of the upper electrode. Because the tunnelingprobability is spin dependent, the current depends upon the relativeorientation of the magnetizations of magnetic layers above and below thebarrier layer. Most advantageously, one of the two magnetic layers (thepinned layer) in the MTJ has its magnetization fixed in direction, whilethe other layer (the free layer) has its magnetization free to move inresponse to an external stimulus. If the magnetization of the free layeris allowed to move continuously, as when it is acted on by acontinuously varying external magnetic field, the device acts as avariable resistor and it can be used as a read-head. If themagnetization of the free layer is restricted to only two orientationsrelative to the fixed layer (parallel and anti-parallel), the first ofwhich produces a low resistance (high tunneling probability) and thesecond of which produces a high resistance (low tunneling probability),then the device behaves as a switch, and it can be used for data storageand retrieval (a MRAM).

Magnetic tunneling junction devices are now being utilized asinformation storage elements in magnetic random access memories (MRAMs).Gallagher et al. (U.S. Pat. No. 5,640,343) discloses an array of MTJelements connected to a diode in series, the whole comprising an MRAMarray. The individual MTJ elements are substantially formed as describedbriefly above. As is further disclosed by Gallagher, when used as aninformation storage or memory device, a writing current (or currents)orients the magnetization of the free layer so that it is eitherparallel (low resistance) or anti-parallel (high resistance) to thepinned layer. The low resistance state can be associated with a binary 0and the high resistance state with a binary 1. At a later time a sensingcurrent passed through the MTJ indicates if it is in a high or lowresistance state, which is an indication of whether its magnetizationsare, respectively, antiparallel or parallel and whether it is in a 0 or1 state. Typically, switching the magnetization direction of the freelayer from parallel to antiparallel and vice-versa is accomplished bysupply currents to orthogonal conductor lines, one which is above theMRAM cell and one which is below it. The line above the cell is referredto as the “digit” or “word” line and is electrically isolated from thecell by intervening dielectric material. The line below the cell, calledthe “bit” line, is in electrical contact with the top of the cell and isused for both writing (changing free layer magnetization) and reading(detecting high or low resistance). The word line is oriented so thatits magnetic field is along the hard axis of the free layer. The bitline provides the component of the switching field parallel to the easyaxis of the free layer. The two lines intersect orthogonally with thecell lying between them so that the combined field peaks just above theswitching threshold of the cell (field required for a transition fromparallel to antiparallel, or vice versa, relative orientations of thefree and pinned layer magnetizations). For fast operation of the cell,it must have a high magnetoresistance ratio (DR/R), where DR representsthe resistance variation when the free layer magnetization switchesdirection and R represents the total minimum resistance of the cell whenfree and pinned layers are magnetized in parallel directions. For stableoperation, the cell's junction resistance, RA, where A is cellcross-sectional area, must be well controlled. When the MRAM device isused as the basic element of a memory, it is replicated to form an arrayof many such devices and integrated with associated CMOS circuitry whichaccesses particular elements for data storage and retrieval.

When fabricating an MRAM element or an array of such elements, thenecessity of creating a high value of DR/R and maintaining a high degreeof control over the junction resistance requires the formation of thin,smooth layers of high quality.

In a standard MRAM array structure the MTJ stack (lower electrode/AlOxtunneling barrier/upper electrode) is deposited on top of the bottomconductor (the bit line), which is a tri-layer such as Ta/Cu/Ta orNiCr/Ru/Ta. The lower electrode is a magnetically pinned layer, theupper electrode is a magnetically free layer and the tunneling barrierlayer is a layer of oxidized aluminum. Great efforts have been made intrying to control the oxidation of the aluminum when forming the barrierlayer. Typically, the Al layer is formed on the bottom electrode byphysical vapor deposition (PVD). This form of deposition produces a thinlayer of polycrystalline aluminum. Depending on the thickness of thealuminum layer, different forms of oxidation have been used. Forexample, natural oxidation (NOX), plasma oxidation and radical oxygenoxidation (ROX) have all been used to produce the barrier layer and willbe discussed further below.

A typical tunneling barrier layer for an MRAM device is made by in-situoxidation of a 7 to 10 angstrom thick Al layer and the resultingoxidized layer has a junction resistance, RA, in the kilo-ohm-micron²(kΩμm²) range. When the oxidation method used is plasma oxidation, theenergetic oxygen plasma ions may damage the underlying ferromagneticmaterial of the lower (pinned) electrode. Therefore, radical oxidation(ROX) is normally used for the oxidation method. ROX is achieved bycovering the plasma with a grounded metal mesh “shower cap,” so thatonly the oxygen radical and neutral oxygen can reach the substrate. Inthe initial stage of ROX, oxygen covers the aluminum grain surfacehomogeneously and the resulting oxidized structure is amorphous.Oxidation starts at the Al surface and forms a good Al₂O₃ stoichiometry.The oxidation process then moves progressively downward to the interfacebetween the deposited aluminum layer and the underlying electrodesurface. It is known that oxygen diffusion proceeds much more rapidlyalong the grain boundary than into the grain itself. Consequently, theoxygen diffusion front does not proceed at a uniform rate or with auniform spatial dependence through the deposited aluminum layer. Adiscussion of several oxidation methods can be found in Y. Ando et al.,“Growth mechanisms of thin insulating layer in ferromagnetic tunneljunctions prepared using various oxidation methods,” J. Phys. D.: Appl.Phys., Vol. 35, 2415–2421, (2002).

When the Al layer is “under-oxidized,” meaning that the portion of thelayer closest to the interface with the bottom electrode has an oxidestoichiometry of the form Al₂O_(x), with x<3, as is the case in NOX(without the assist of a plasma), the product RA is low, and so are thelayer breakdown voltage and the GMR ratio, DR/R. When the layer is“over-oxidized,” meaning that oxygen has diffused into the lowerelectrode, the product RA is greatly increased, but DR/R is decreased.The use of plasma oxidation to produce oxidized layers is discussed inHeejae Shim et al., “Magnetic tunnel junctions with a tunnel barrierformed by N₂O plasma,” Appl. Phys. Lett., Vol. 83, No. 22, p. 4583, 1Dec. 2003.

After the MRAM film stack is formed (the multi-layered lamination oflayers before patterning), it is thermally annealed to fix themagnetiization direction of the pinned ferromagnetic layer (the lowerelectrode). Annealing improves the homogeneity of the oxidized aluminumlayer by redistributing the oxygen in the barrier layer and by drivingout the oxygen from the pinned layer. It is found that the thermalannealing process improves the integrity of the barrier layer (eg. itraises the breakdown voltage) and enhances the DR/R ratio.

In order to obtain a high DR/R, the ferromagnetic layers adjacent to thebarrier layer are formed of CoFe. It has been reported that CoFe with25% Fe by number of atoms yields a higher DR/R than CoFe with 10% Fe bynumber of atoms. This is due to the fact that the CoFe(25%) produces ahigher degree of spin polarization of conduction electrons at theCoFe/Al₂O_(x) interface. Experiments have also shown that an electrodeformed of NiFe(60%) also gives a high DR/R and, in addition, because thebinding energy between Fe and O is weaker than that of Co and O, theannealing process drives oxygen out of a NiFe electrode more readilythan a CoFe electrode.

In the fabrication of MTJ MRAM devices it would be highly desirable toform an Al₂O_(x) tunneling barrier layer that is flat and smooth and hasan Al₂O₃ stoichiometry at its upper and lower interfaces with theelectrodes. In this case, the spin polarization would be symmetrical atboth interfaces, yielding both a high DR/R and breakdown voltage.

The present invention discloses a novel oxidation technique for formingan improved Al₂O_(x) barrier layer. The invention is to do the oxidationfrom both sides of the deposited Al layer, so that the Al₂O₃stoichiometry is ultimately more uniformly achieved within the entirebody of the layer. The method that is proposed to produce thissymmetrical oxidation process is to form an oxygen surfactant layer(OSL) on the surface of the CoFe(25%) or NiFe(60%) pinned layer, so thatthere is a source of oxygen for the bottom surface of the deposited Allayer. An oxygen surfactant layer, which is discussed in relatedApplications HT 02-032 and HT 03-006, both of which are fullyincorporated herein by reference, is a sub-monolayer of oxygen adsorbedon the surface of a deposited layer. When the Al layer is then subjectedto a ROX process, the plasma supplies oxygen to the exposed Al surface,while the surfactant layer supplies it to the “hidden” surface. It isnoted that reactivity of oxygen is stronger with Al than with CoFe, sothe oxygen in the OSL will diffuse into the Al layer to form aCoFe/Al₂O₃ interface.

SUMMARY OF THE INVENTION

A first object of this invention is to provide a method of forming anMTJ MRAM element and an array of such elements, that are characterizedby a smooth, flat tunneling barrier layer formed between the bottom andtop electrodes.

A second object of this invention is to provide such a method that alsoproduces an MTJ MRAM element and array of such elements that arecharacterized by a high DR/R ratio and a high breakdown voltage of thetunneling barrier layer.

A third object of the present invention is to provide the MTJ MRAMelement and array of such elements that are produced by the method.

The objects of the present invention will be achieved by the fabricationof an MRAM element wherein the tunneling barrier layer is an oxidizedaluminum layer having a uniform Al₂O₃ stoichiometry. The uniformstoichiometry is achieved by subjecting the as-deposited Al layer, whichis deposited by physical vapor deposition (PVD) to an in-diffusion ofoxygen from both its interface with the bottom electrode on which it hasbeen deposited and its exposed upper surface. The source of oxygen fromthe bottom electrode is an oxygen surfactant layer (OSL), which is amonolayer of oxygen adsorbed on the upper surface of the bottomelectrode. In accord with the method of this invention, the bottomelectrode is a pinned ferromagnetic layer of either CoFe(25%) alone, ora bi-layer of CoFe(10%)-NiFe(60%). Because of the relative reactivitiesof Fe and Al with oxygen, either of these ferromagnetic layers have theproperty of being able to release oxygen atoms adsorbed on their surfaceto newly arriving Al atoms being deposited by the PVD process.

In order to achieve the full advantages of the present method, it wasnecessary to demonstrate, experimentally, the role of an oxygensurfactant layer (OSL) as a source of oxygen during the deposition of anAl layer. A simple multi-layer structure was used to test the basicinvention idea. The test structure is:Ta 50/Ru 10/CoFe(25%)30/OSL/NiCr 50.In the structure above, the Ta 50/Ru 10/CoFe(25%) 30 is a bottomelectrode (the numbers representing thicknesses in angstroms), the Ta/Rubeing a conducting lead layer and the CoFe being the ferromagneticpinned layer. Of course, the actual pinning structure is not present,since the CoFe is only being tested for its ability to release oxygenfrom the surfactant layer, which is represented as “OSL” above.

To form the structure above, the Ta/Ru/CoFe electrode is first sputteredin a PVD module. The sputtered formation is then transferred to an“oxidation” chamber, which in the present experiment is a low pressure,commercially available Anelva 7100 system. The oxidation source in thechamber is very low pressure oxygen gas, specifically oxygen at apressure of approximately 2×10⁻⁷ torr, which is fed into the chamber at0.02 sccm.

As can be seen from the table below, we exposed the CoFe layer to fourdifferent oxygen flow rates (0 sccm, 0.02 sccm, 0.04 sccm and 0.30 sccm)and corresponding exposure times (0.0 sec, 300 sec, 300 sec and 30 sec).The resulting CoFe layer was tested for its saturation magnetization,B_(s), its coercivity, H_(c), and for the change in B_(s) produced bythe treatment.

Flow Rate Exposure time B_(s) H_(c) (Oe) B_(s) change  0.0 (no oxygen)0.0 0.5391 13.21   0.00% 0.02 sccm 300 sec 0.5591 10.59   3.71% 0.04sccm 300 sec 0.5616 10.45   4.27% 0.30 sccm  30 sec 0.5014 13.99 −6.98%

Because the oxygen source provided by the OSL readily reacts with Alatoms being deposited on the OSL, the Al₂O₃ begins to form immediately.As the initial layer of Al₂O₃ is amorphous, the epitaxial growth of theAl on the CoFe is interrupted (ie. it has no crystalline sublayer topromote large grain growth). As a result, the remaining Al layer is flatand smooth because whatever crystal grains grow are very small. The OSLcan also be formed by sputtering the CoFe (or whatever ferromagneticlayer is used) using an oxygen doped argon gas. HT 03-006, cited aboveand fully incorporated herein by reference, discloses the use of oxygendoped argon gas in sputter deposition of Cu spacer layers in theformation of GMR read sensors. It has been found that the small amountof oxygen that is incorporated within the sputtered layer is highlymobile and diffuses to the layer surface to form the OSL.

Once it is established that the OSL provides the oxygen needed toproduce the desired high quality tunneling barrier layer, twoadvantageous multilayered stack configurations within which to apply themethod are found to be the following:BL/SE/NiCr/MnPt/CoFe(10%)/Ru/CoFe(25%)/OSL/Al/ROX/CoFe(25%)-NiFe(20%)/Ta  (A)BL/SE/NiCr/MnPt/CoFe(10%)/Ru/CoFe(10%)-NiFe(60%)/OSL/Al/ROX/NiFe(60%)-NiFe(20%)/Ta  (B)

In both (A) and (B), BL stands for “bottom lead,” SE stands for “sputteretching,” OSL stands for “oxygen surfactant layer” and ROX stands for“radical oxidation.” The mild ROX process applied to oxidize the uppersurface of the Al layer also enhances the overall homogeneity andstoichiometry of the barrier layer, making the interfacial regionsparticularly high quality. It is further noted that stack (A) includes aCoFe(25%) layer on which the OSL is formed, while stack (B) includes acomposite CoFe(10%)-NiFe(60%) layer on which the OSL is formed.

After the stack configurations are formed, they are annealed forapproximately 5 hours in a 10 kOe (kilo-Oersted) magnetic field to setthe pinning fields. This annealing process further homogenizes theoxygen in the barrier layer to improve its integrity. In this regard,the smaller grain size already produced in the Al layer as a result ofthe OSL enhances the homogenization process of the anneal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a–e are schematic cross-sectional views of the formation of anMTJ MRAM element using the method and configuration of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1 a, there is seen in a schematic cross sectionan initial stage of a preferred embodiment of the invention, theformation of a single MRAM element, which can be a part of an array ofsuch elements. It is to be understood that in the embodiments to bedisclosed in what follows, all layer depositions take place in a highvacuum PVD chamber suitable for depositing thin layers by sputtering andoxidation processes take place in a separate plasma oxidation chamber.In these embodiments the system was a commercially available Anelva 7100system which includes both such chambers, but other comparable systemsare also suitable.

There is shown first a substrate (10), which in this embodiment is alower conducting lead (the bit line, for example) on which the MRAMelement will be formed. It is further understood that the single MRAMelement can be one of an array of such elements and that such element orarray may be further connected to associated circuitry used in storingand retrieving information.

The conducting lead layer (10) is typically a multilayer formation suchas Ta/Ru/Ta and it is found that by subjecting the second Ta layer (15)(a capping layer), originally formed to a thickness betweenapproximately 80 and 100 angstroms, with a sputter-etching (SE) processwhich removes approximately 20 to 30 angstroms of that Ta layer,subsequently formed layers are smoother and more uniform. Thissmoothness-promoting property of the sputter-etched layer is disclosedin related Application HT 03-022, which is fully incorporated herein byreference.

Referring to FIG. 1 b, there is shown a NiCr seed layer (20) is thenformed on the sputter-etched Ta layer surface, that thinner Ta layer nowdenoted (17). The seed layer further enhances smooth layer overgrowth asis set forth in related Application HT 03-025, fully incorporated hereinby reference. A bottom electrode (30) is then formed on the seed layer,which in this embodiment is an antiferromagnetic pinning layer (32),which is preferably a layer of MnPt formed to a thickness betweenapproximately 100 and 200 angstroms, on which is formed a syntheticantiferromagnetic pinned (SyAP) tri-layer structure comprising a lowerferromagnetic layer (34), a coupling layer (36) and an upperferromagnetic layer (38), the two ferromagnetic layers subsequentlybeing magnetized in antiparallel directions in the annealing processalready discussed. The lower ferromagnetic layer is a layer of CoFe(10%)formed to a thickness between approximately 15 and 25 angstroms with 25angstroms being preferred. On this layer is formed a thin coupling layer(36) of Ru, which is formed to a thickness between approximately 7 and 8angstroms with 7.5 angstroms being preferred. On the coupling layer isformed the upper ferromagnetic layer (38) of CoFe (25%) with a thicknessbetween approximately 15 and 20 angstroms. The 25% by atom number of Fein this layer of CoFe is found to produce a particularly good value ofDR/R. Alternatively, the upper ferromagnetic layer can be a compositelayer of CoFe(10%)-NiFe(60%) (NiFe over CoFe), which is formed to athickness between approximately 5 and 10 angstroms to produce aneffective magnetic thickness (product of magnetic moment and thickness)equivalent to 15 to 20 angstroms of CoFe(25%). On the upperferromagnetic layer (38), of either form, there is then formed the OSL(39) which is an essential part of the present invention. The OSL can beformed within an oxidation chamber after the upper layer of CoFe orCoFe—NiFe is formed or, as previously discussed, the OSL can be formedintegrally with the upper layer by sputtering the layer using argonadmixed with a small amount of oxygen. If the OSL is formed in anoxidation chamber, the oxygen source should preferably be present atvery low pressure of approximately 2×10⁻⁷ torr and should be maintainedby an oxygen inflow of between approximately 0.02 and 0.04 sccm for atime of approximately 300 sec. The resulting OSL is less than amonolayer of oxygen.

If the OSL is to be formed as the CoFe or CoFe—NiFe layer is deposited,either layer can be sputter-deposited using a mixture of argon andoxygen in a manner set forth in detail in related Application HT 03-006.

Referring now to FIG. 1 c, there is shown the formation of a thin, flatand smooth tunneling barrier layer (50) of homogeneous Al₂O₃stoichiometry on the pinned layer. First, an Al layer betweenapproximately 7 and 10 angstroms thickness with approximately 9angstroms being preferred is formed on the OSL of the CoFe(25%) layer(38). As this layer is first being deposited, oxygen atoms from the OSL(39) are being adsorbed by the Al atoms and are forming a very thinamorphous interfacial region (51) of substantially stoichiometric Al₂O₃.As the deposition continues, the oxygen from the OSL becomes exhaustedand the remaining Al layer (53) is formed of small grained crystallineregions because the amorphous nature of the Al₂O₃ interfacial region(51) prevents the formation of large Al grains.

Referring next to FIG. 1 d, there is shown the Al layer being subjectedto a radical oxidation (ROX), which is oxidation by a shower of oxygenradicals, atoms and plasma generated ions in a separate plasma chamber.This oxidation process causes the upper small grained Al layer ((53) inFIG. 1 c) to become oxidized with a good Al₂O₃ stoichiometry whichextends inward to the Al₂O₃ layer (51) produced by adsorption of theOSL. This ROX layer is now denoted (58). The complete Al layer (50) isnow substantially uniformly and homogeneously oxidized. The OSL (39) isgone, having contributed its oxygen content to the Al layer. The ROXprocess will not be discussed herein in detail since it is discussed inthe paper by Y. Ando cited above and functionally provided by theoperation of a plasma chamber within the Anelva unit discussed above.Briefly, the ROX process as applied to achieve the objects of thepresent invention is a plasma oxidation process carried out within aplasma oxidation chamber wherein a grid-like cap is placed between anupper electrode and the wafer surface being oxidized. Oxygen gas is thenfed to the upper electrode and power is supplied to the electrode to atleast partially ionize the gas. Passage through the cap renders theoxygen atoms, molecules, radicals and ions produced by the electrodeless energetic when they arrive at the wafer surface. Within the plasmachamber used herein, an upper electrode within the chamber is fed with0.5 liters of oxygen gas to produce a shower of oxygen radicals. Poweris supplied to the electrode at a rate of 500 to 800 watts.

Referring now to FIG. 1 e, there is seen the formation of FIG. 1 c nowhaving been returned to the PVD chamber for the deposition of the freelayer (60) on the homogeneously oxidized barrier layer (50). The freelayer is preferably a bilayer of NiFe (60%)-NiFe(20%) in which the firstNiFe layer is formed to a thickness between approximately 5 and 10angstroms with 10 angstroms being preferred and the second NiFe layer isformed to a thickness between approximately 25 and 50 angstroms with 30angstroms being preferred, or a bilayer of CoFe(25%)-NiFe(20%) with theCoFe being between approximately 5 and 10 angstroms with 10 angstromsbeing preferred and the NiFe being between approximately 25 and 50angstroms with 30 angstroms being preferred. A capping layer (65) of Ta,formed to a thickness between approximately 150 and 300 angstroms isthen formed on the free layer. Although it is not represented in thefigures, there is then an anneal to set the pinned layer magnetizationdirections, carried out at approximately 280° C., for approximately 5hours in an external magnetic field of approximately 10 kOe. The lengthyhigh temperature processing serves to further homogenize the oxidationof the barrier layer (50), which is further enhanced by the small Algrain size resulting from the underlying OSL. The layer (50) is,therefore, shown uniformly shaded.

As is understood by a person skilled in the art, the preferredembodiments of the present invention are illustrative of the presentinvention rather than limiting of the present invention. Revisions andmodifications may be made to methods, materials, structures anddimensions employed in forming and providing an MTJ MRAM device in whicha tunneling barrier layer of uniform and homogeneous Al₂O₃ stoichiometryis formed by radical oxidation of an Al layer deposited on a lowerelectrode having an oxygen surfactant layer, while still forming andproviding such a device and its method of formation in accord with thespirit and scope of the present invention as defined by the appendedclaims.

1. A method of forming a magnetic tunneling junction (MTJ) MRAM devicecomprising: providing a substrate; a formation process of forming, in ahigh vacuum deposition system, a bottom conductor layer on saidsubstrate, said formation process further comprising: forming aconducting lead layer on said substrate; forming a Ta capping layer onsaid metal layer; and sputter-etching said Ta capping layer; forming, inthe same high vacuum deposition system a lower pinned electrode, saidformation further comprising: forming an NiCr seed layer on saidsputter-etched Ta layer; forming, an AFM pinning layer on said seedlayer; forming a synthetic antiferromagnetic pinned (SyAP) layer on saidpinning layer, said formation comprising a lower ferromagnetic layerformed on said pinning layer, a coupling layer formed on said lowerferromagnetic layer and an upper ferromagnetic layer formed on saidcoupling layer; forming, in an oxidation chamber an oxygen surfactantlayer on said upper ferromagnetic layer; forming, a tunneling barrierlayer on said oxygen surfactant layer, said formation furthercomprising: forming, in said high vacuum deposition system, a layer ofAl on said oxygen surfactant layer, said deposition first causing theadsorption of substantially all oxygen from said surfactant layer intosaid Al layer to form an amorphous layer of stoichiometric Al₂O₃ and,upon the depletion of all said oxygen in said surfactant layer, theremainder of said deposition forming a flat and smooth Al layer of smalland uniform grain size; then oxidizing said flat and smooth Al layer ina plasma oxidation chamber by a process of radical oxidation, saidprocess forming from said flat and smooth Al layer an oxidized layer ofstoichiometric Al₂O₃, said oxidized layer extending to said amorphouslayer of stoichiometric Al₂O₃ formed during said Al deposition, to form,thereby, a tunneling barrier layer of substantially homogeneous Al₂O₃stoichiometry; and forming, in said high vacuum system a free layer onsaid tunneling barrier layer; forming, in said high vacuum system anupper capping layer on said free layer; annealing said MTJ MRAM deviceto magnetize said pinned layer, said annealing process further enhancingthe Al₂O₃ stoichiometry of the tunneling barrier layer.
 2. The method ofclaim 1 wherein said NiCr seed layer are formed of NiCr having 35%–45%Cr by number of atoms.
 3. The method of claim 1 wherein the cappinglayer of Ta is formed to a thickness between approximately 80 and 100angstroms and is sputter etched in a process to remove betweenapproximately 20 and 30 angstroms of said Ta layer.
 4. The method ofclaim 1 wherein the AFM antiferromagnetic pinning layer is formed as alayer of MnPt to a thickness between 100 and 200 angstroms or a layer ofIrMn formed to a thickness between 50 and 100 angstroms.
 5. The methodof claim 1 wherein the SyAP layer is formed as a lower and upper layerof CoFe separated by a layer of Ru and wherein at least the upper CoFelayer, which is adjacent to said tunnel barrier layer, is CoFe(25%). 6.The method of claim 1 wherein the SyAP layer is formed as a lower layerof CoFe and an upper composite layer of CoFe(10%)-NiFe(60%) separated bya coupling layer of Ru, wherein the upper composite layer is adjacent tothe tunnel barrier layer.
 7. The method of claim 5 wherein the lowerlayer of CoFe is formed between approximately 18 and 25 angstroms thick,the upper layer of CoFe is formed between approximately 15 and 20angstroms thick and the Ru layer is formed between approximately 7 and 8angstroms thick.
 8. The method of claim 6 wherein the lower layer ofCoFe is formed between approximately 18 and 25 angstroms thick, theupper composite layer of CoFe(10%)-NiFe(60%) is formed with theNiFe(60%) being between approximately 5 and 10 angstroms thick, givingsaid composite layer a total magnetic thickness equivalent to 15 to 20angstroms of CoFe(25%) and the Ru layer is formed between approximately7 and 8 angstroms thick.
 9. The method of claim 1 wherein the process offorming an oxygen surfactant layer on said upper ferromagnetic layerfurther comprises introducing oxygen into said oxidation chamber at arate of between 0.02 and 0.04 sccm to purge said chamber with oxygen gasat approximately 2×10⁻⁷ torr pressure and leaving the layer in theoxidation chamber for approximately 2 minutes.
 10. The method of claim 1wherein the process of forming an oxygen surfactant layer on said upperferromagnetic layer further comprises sputtering said layer with argonatoms in an oxygen ambient wherein the sputtering chamber maintains abase pressure of approximately 5×10⁻⁹ torr and said ultra-low pressureAr/O₂ mixture is produced by mixing an ultra-low pressure source of highpurity Ar containing oxygen in an amount less than 0.5 ppm, with thesame Ar source to which between approximately 400 and 600 ppm of oxygenhas been admixed, said high purity Ar being at an approximate pressureof 0.4 millitorr and said oxygen having therein a partial pressure ofbetween approximately 10⁻⁹ and 10⁻⁸ torr.
 11. The method of claim 1wherein said radical oxidation process further comprises: feeding 0.5liters of oxygen gas to an ionizing electrode within a plasma chamber;partially ionizing said oxygen at an electrode supplied with betweenapproximately 500–800 watts of power; passing said partially ionized gasthrough a grid to produce a shower of oxygen species comprising oxygenmolecules, atoms, ions and radicals; directing said shower at said Allayer being oxidized.
 12. The method of claim 1 wherein the free layeris formed as a bilayer of CoFe(25%)-NiFe(20%) in which the CoFe(25%) isformed to a thickness between approximately 5 and 10 angstroms and theNiFe(20%) is formed to a thickness between approximately 25 and 50angstroms.
 13. The method of claim 1 wherein the free layer is formed asa bilayer of NiFe(60%)-NiFe(20%) in which the NiFe(60%) is formed to athickness between approximately 5 and 10 angstroms and the NiFe(20%) isformed to a thickness between approximately 25 and 50 angstroms.